Migrate language block 46 - canonical_const ... char_escape.

tests/language_2/char_escape_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Dart test for reading escape sequences in string literals
 
 import "package:expect/expect.dart";
 
 class CharEscapeTest {
   static testMain() {
     var x00 = "\x00";
@@ skipping 513 matching lines @@
     Expect.equals("\W", "W");
     Expect.equals("\X", "X");
     Expect.equals("\Y", "Y");
     Expect.equals("\Z", "Z");
   }
 }
 
 main() {
   CharEscapeTest.testMain();
 }